What is a good monologue given by the character Malcolm in Macbeth?

The character of Malcolm has a few good monologues in Macbeth, although some of them are the most cryptic and ambiguous monologues in the entire play (specifically, Malcolm's monologues in Act 4). 

Arguably, Malcolm's first monologue takes place after he finds out his father has died. It is an aside to his brother, Donalbain:

MALCOLM: What will you do? Let's not consort with them. / To show an unfelt sorrow is an office /...

The character of Malcolm has a few good monologues in Macbeth, although some of them are the most cryptic and ambiguous monologues in the entire play (specifically, Malcolm's monologues in Act 4). 

Arguably, Malcolm's first monologue takes place after he finds out his father has died. It is an aside to his brother, Donalbain:

MALCOLM: What will you do? Let's not consort with them. / To show an unfelt sorrow is an office / Which the false man does easy. I'll to England... / This murderous shaft that's shot / Hath not yet lighted, and our safest way / Is to avoid the aim. Therefore to horse, / And let us not be dainty of leave-taking / But shift away. There's warrant in that theft / Which steals itself when there's no mercy left. (II.iii.160-172)

In this monologue, Malcolm accurately foresees that he and Donalbain are in danger and that the two of them should quickly flee to safety. After this moment, Malcolm is not seen again until later in the play. When he is seen again, Malcolm is engaging with Macduff. He tricks Macduff, stating he is more of a monster than Macbeth, to test Macduff's loyalties. Malcolm claims that:

MALCOLM: It is myself I mean, in whom I know / All the particulars of vice so grafted / That, when they shall be opened, black Macbeth / Will seem as pure as snow, and the poor state / Esteem him as a lamb, being compared / With my confineless harms. (IV.iii.61-66)

At face value, these words are confusing and seem contrary to the Malcolm the audience has first seen. However, it soon becomes clear that Malcolm is testing Macduff, which proves Malcolm to be a cunning and intelligent future leader.

It also should be noted that Malcolm has the final lines in Macbeth. Malcolm ultimately represents the new restored order. His final monologue, which can be found at the very end of the play, is a beautiful testament to patriotism, community and unity.